OBJECTIVE: To support key investigators conducting a multidisciplinary program of basic research on the etiology and pathogenesis of cancer with special reference to mammary tumors in mice and women and the role of somatic mutation and of genetic damage. APPROACH: Mammary cancer of mice provides an in vivo model system and cell culture of mouse and human mammary tumors provide in vitro model systems which closely simulate human breast cancer in many respects. Cell cultures provide model systems for somatic mutation and genetic damage in human leukemia. The disciplines collaborating in these studies are immunology, molecular biology, cell biology, biophysics, cytogenetics, virology and biochemistry. RECENT PROGRESS: Of the 5 glycoproteins found in purified mouse mammary tumor virus, 2 have been identified in human milk by serologic tests, confirming previous evidence of a transcriptase, leukocyte sensitization, and morphology. Mice can be protected with a killed vaccine made of purified whole virus and by purified extracts of viral glycoproteins.